Peronospora is a genus of plant pathogens, belonging to the class of water moulds. Water moulds are not true fungi (Eumycota) since they belong to the kingdom of chromalveolates.
There are about 75 species in the genus, mostly specific to genera or families of herbaceous dicotyledonous plants. One of the best known Peronospora species (Peronospora parasitica, on Brassicaceae) has now been shown to be a species complex in the genus Hyaloperonospora. The most important plant pathogen in this complex, on Brassica, is now known as Hyaloperonospora brassicae (and does not appear in the list below).